(a) Technical Field
The present disclosure relates generally to a method and an apparatus for generating a torque command and, more particularly, to a method and an apparatus for generating a torque command capable of correcting a torque loss amount and a torque excess amount due to a threshold increase rate and a threshold decrease rate.
(b) Description of the Related Art
As is generally known in the art, a hybrid electric vehicle uses an internal combustion engine and a battery power source together. The hybrid electric vehicle efficiently combines the torque from the internal combustion engine and torque from the motor.
In general, a hybrid electric vehicle includes an engine, a motor, an engine clutch controlling torque between the engine and the motor, a transmission, a differential gear device, a high voltage battery, a hybrid starter & generator (HSG) starting the engine or generating power according to output of the engine, and wheels. The HSG may refer to an integrated starter & generator (ISG).
Additionally, a hybrid electric vehicle enables driving in an electric vehicle (EV) mode, in which only torque of the motor is used; a hybrid electric vehicle (HEV) mode, in which torque of the engine is used as main torque and torque of the motor is used as auxiliary torque; and a regenerative braking mode, in which braking and inertial energy are recovered through electrical power generation of the motor during braking of the vehicle or during driving of the vehicle by inertia to be charged in the battery. The HEV mode is enabled by engaging or releasing the engine clutch depending a manipulation of an accelerator pedal or a brake pedal by a driver, a vehicle speed, a state of charge (SOC) of the battery, and the like. By using both mechanical energy of the engine and electrical energy of the battery, using optimal operation regions of the engine and the motor, and recovering the energy upon braking, fuel efficiency in a hybrid electric vehicle may be improved and the energy of the hybrid electric vehicle may be efficiently used.
A torque source, such as the engine, the motor, or the HSG, generates torque based on a torque command. In the case of the hybrid electric vehicle, an engine torque command and a motor torque command are determined based on a vehicle speed, a position of the accelerator pedal (i.e., pushed degree of the accelerator pedal), an engine speed, a motor speed, and the like. However, due to a performance limitation of the torque source (e.g., a tension limitation of a belt connecting the engine and the HSG, and a bandwidth of the motor), torque corresponding to a torque command may not be able to be generated. An increase rate and a decrease rate of the torque command are limited in order to prevent the torque source from being damaged.
In this regard, FIG. 7 is a graph illustrating a conventional HSG torque command. As shown in FIG. 7, when torque of the HSG is rapidly increased or decreased, a threshold increase rate and a threshold decrease rate are applied to the HSG torque command, i.e., since the belt connecting the engine and the HSG may be snapped. As a result, performance and behavior of the HSG is deteriorated since a torque loss amount and a torque excess amount are generated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the related art that is already known to a person of ordinary skill in the art.